This invention pertains to apparatus and methods for removing heating or cooling fluid from a rotary heat exchange device. Particularly, it relates to an apparatus and methods for removing condensate from a steam heated screw press.
Many heat exchange devices such as drying drums or heated screw presses use internally injected steam to heat a rotating body, which in turn contacts the processed materials. In this process, the steam condenses within the apparatus, leaving condensate in the rotating body. This condensate must be removed in some fashion.
It is advantageous to minimize the amount of condensate present in a steam-heated screw press or drum. High efficiency in a heat exchanger may be attained only by minimizing the amount of condensate. It is desirable to remove only condensate from the heat exchange device and to prevent uncondensed steam from exiting the shell or drum. Escaping steam lowers the efficiency of the exchanger.
Moreover, the steam inlet and condensate outlet arrangements should not unduly complicate the construction of the apparatus, or cause other problems. For example, the rotating element of the apparatus normally must be driven by a shaft attached at one end of the element. It is therefore desirable to introduce steam and remove condensate at the other end. The steam circulation system, however, should assure that steam circulates throughout the axial extent of the rotating member, to both ends, and should remove condensate effectively from those portions remote from the steam inlet and outlet end.
Various arrangements have been proposed for accomplishing these tasks.
Sato, U.S. Pat. No. 3,939,763, discloses a rotating screw press with a tapered hollow shell and a condensate removal system. Steam flows from a steam inlet disposed at the small end of the screw drum, through a rotary coupling, and partially into the shaft. The steam vents out of the shaft and into the hollow shell. Cooled vapor is exhausted at the opposite end of the screw drum. The vapor enters into the shaft, flows out the drum, and is collected by a steam trap external to the drum. The shaft is substantially solid, particularly between the input and output heat exchange fluid conduits disposed at opposite ends of the shaft.
Solheim, U.S. Pat. No. 2,883,163, discloses a rotating heat exchanger having a hollow cylinder surrounded by hollow helical threads. The inside chamber of each thread is divided in half by a partition plate. Steam enters directly into the threads, heats the threads and surrounding material, and condenses. The condensate collects within the threads until the partition plate rotates into a substantially vertical position. Any condensate captured by the partition plate flows into the hollow cylinder via a stub pipe extending between the cylinder and threads. The condensate within the cylinder is evacuated by a siphon pipe.
Dix, U.S. Pat. No. 1,900,166 discloses vanes for discharging a liquid from a hollow drum or cylinder. Fins are disposed at the end of the drum closest to the condensate outlet. As the drum rotates, the fins guide the liquid from the circumference of the drum to an opening in the center of the end of the drum shell. This opening is directly connected to the condensate outlet. In other words, liquid is scooped from the bottom of the drum and flows directly into a discharge pipe.
Mayer, U.S. Pat. No. 1,837,562, also discloses vanes for discharging liquid from a hollow drum. The vanes scoop condensate from the bottom of the drum, and move the condensate towards an opening disposed in the center of the drum at the end opposite of the steam inlet. The condensate flows directly out a condensate outlet.
Despite this art, there is still need for further improvement.